What is the block diagram of a first-order system?

A first-order system is characterized by having a single time constant and is represented by a first-order ordinary differential equation.
The block diagram of a first-order system consists of an input, the transfer function H(s), and an output.
In the block diagram of a first-order system, R(s) is the input (or reference signal), H(s) is the transfer function of the first-order system, and C(s) is the output (or system response).